The present invention relates to an intake device for an internal combustion engine, and more particularly to an improvement in an intake device including an intake passage provided with an air flow meter.
Referring to FIGS. 1 and 2, a prior art intake device will be described hereinafter. In the case of an Electronic Fuel Injection (EFI) system, it is the ordinary practice to control the quantity of fuel per each injection from an injector 4 (fuel injection valve) via a control circuit in response to a detect signal produced by an air flow meter (air flow sensor) 3, such as a Karman vortex type air flow meter or a heat wire type air flow meter, mounted to an intake passage 2 upstream of a throttle valve 1, to control the air/fuel ratio. Air passing through an air cleaner 5 flows through a honeycomb rectifier 7 positioned at the air flow meter inlet duct 6, then flows through a Karman vortex generator 3a to produce regulated vortex. With a heat wire type sensor incorporated in the vortex generator 3a, the generation frequency increases in proportion to the velocity of air and is detected and fed to the control circuit as its detect signal. Air passing through the vortex generator 3a flows through an air flow meter outlet duct honeycomb rectifier 8 and into an engine combustion chamber 10 via the throttle valve 1, injector 4 and intake valve 9. Also shown are a microprocessor 11 and a baffle plate 12 for fuel atomization. The air flow meter duct 6 comprises a tube having a rectangular section for stabilizing the vortex. This has necessiated providing two cylindrical adapters 13 and 14 secured to ends of the duct 6, to allow connection with the air cleaner 5 via a rubber duct 15 and with a throttle body 17 via a rubber duct 16.
The conventional intake device described above wherein various kinds of joints, such as adaptors 13, 14 must be employed for installation has a disadvantage that the piping is complicated, creating bulk and increasing cost. Where, as shown in FIG. 2, a single point injection (SPI) type EGI system is employed which uses a single injector 4 for supplying fuel to all of the combustion chambers, despite the demand that the overall system be as compact as a conventional carburetor, such arrangement causes an undesirable increase in overall engine height.